Several products that are prepared for human, veterinary or experimental use may contain unwanted and potentially dangerous contaminants such as viruses, bacteria, yeasts, molds, mycoplasmas and parasites. Consequently, it is of utmost importance that such products are determined to be contaminant free before they are used. This is especially critical when the product is to be administered directly to a patient for example in blood transfusions, organ transplants and other forms of human therapies.
Previously, most procedures have involved methods that screen or test products for a particular contaminant rather than removal of the contaminant from the product. Products that test positive for a contaminant are merely not used. Examples of screening procedures include the testing for a particular virus in human blood from blood donors. However, such procedures are not always reliable. This reduces the value or certainty of the test in view of the consequences associated with a false negative result. False negative results can be life threatening in certain cases, for example in the case of Acquired Immune Deficiency Syndrome (AIDS). Furthermore, in some instances, it can take weeks, if not months, to determine whether or not the product is contaminated.
More recent efforts have focused on methods to remove or inactivate contaminants in the products. Such methods include heat treating, filtration, addition of chemical inactivants and gamma irradiation. It is well documented that gamma irradiation is effective in destroying viruses and bacteria. In fact, one author concludes that gamma irradiation is the most effective method in reducing or eliminating levels of viruses However, when applied to radiation sensitive products, such as blood, gamma irradiation can also have damaging effects on the product itself. In particular, it has been shown that high radiation doses are injurious to red cells, platelets and granulocytes.